182 Dr. Fitton's Instructions 



out any visible alteration at 10 o'clock, but at 6 o'clock the 

 following morning a cylindrical pin had been drawn from the 

 large end of the specimen without separating the fibres. We 

 may therefore safely allow 20,000 pounds for the strength of 

 this oak. 



In a similar manner a pin was drawn out of a specimen of 

 Spanish mahogany, with a load in proportion to 22,000 pounds 

 per square inch, and ash with a load of 16,000 per square inch. 

 It will be observed that my results considerably exceed those 

 of Mr. Barlow ; the dimensions of my specimens were larger 

 than those of Mr. Barlow, and conducted with great care, and 

 with much greater weights to produce fracture. Mr. Barlow's 

 mode of taking the dimensions of his specimens I consider 

 liable to objection, for the silk thread used to measure the cir- 

 cumference of the cylinders would give the diameter too large 

 by the diameter of the thread ; and this quantity would be of 

 considerable moment in affecting the area of the cylinders. 

 I shall probably take an early opportunity of sending you the 

 results of my experiments on the cohesion of various species 

 of wood. Remaining yours truly, 



B. Bevan. 



P. S. If you think the following dimensions of a gourd 

 worth notice, it is at your service. Now growing at Golding- 

 ton in the county of Bedford, in the garden of Mr. Adding- 

 ton, a gourd 5 feet 5 inches in circumference, full 1 1 inches 

 high, supposed to weigh 70 pounds, not at present done 

 growing, — is 8 feet from the root of the vine. 



XXVII. Instructions for collecting Geological Specimens. By 

 William Henry Fitton, M.D. F.R.S. V.P.G.S* 



T T so often happens that specimens sent from distant places, 

 -*- by persons unpractised in geology, fail to give the instruc- 

 tion which is intended, from the want of attention to a few ne- 

 cessary precautions, that the following directions may perhaps 

 be useful to some of those, into whose hands these pages are 

 likely to fall. It will be sufficient to premise, that two of the 

 principal objects of geological inquiry, are, to determine, — 

 1st, the nature of the materials of which the earth is com- 

 posed ; and, 2ndly, the relative order in which these materials 

 are disposed with respect to each other. 



1. Specimens of rocks ought not, in general, to be taken 



* From the Appendix to Captain P. P. King's *' Narrative of a Survey 

 of the Inter-tropical and Western Coasts of Australia." 



from 



